The invention relates to a method and a device for aligning a first steer angle, which is determined continuously in a processor for controlling a steering system, with a second steer angle which is measured continuously by a sensor of the steer system. The invention also relates to a steering system equipped with such a device.
Steering systems have been sufficiently described, in particular power steering systems which, by means of an electric motor, generate an auxiliary force or an auxiliary torque to assist the manual steering force or manual steering torque applied by the driver. So-called steer-by-wire systems have also been described in which there is no continuous mechanical connection between the steering handle (steering wheel) and steering system, but rather an electric motor generates the entire steering torque. In such steering systems, use is often made of a brushless direct-current motor which is operated by means of a sensor arrangement and a control unit connected thereto, in order to generate the required steering torque or auxiliary torque at all times. The transmission to the steering linkage takes place for example via toothed racks or belt drives. As in all steering systems, it is important for the deflection of the steered wheels to take place in a manner dependent as precisely as possible on the desired steer angle. The steer angle is predefined at the steering handle (steering wheel) and can be measured there for example by means of steer angle sensors. The steer angle, measured by separate sensors (and therefore also referred to as external steer angle), is then transmitted for example via signal lines or a data bus (CAN or Flexray) to the controller. The measured steer angle normally deviates from the physical steer angle.
Aside from the measured steer angle, it is also possible, by means of a continuous evaluation (in particular integration) of the rotor position at the electric motor, for a steering angle to be determined (therefore also referred to as internal steer angle). The rotor position is measured for example by means of magneto resistive sensors. The steer angle information gained in this way is required for some functions of the electrical steering system, such as for example for an active return or for artificially generated end stops. Since the system-internal sensors are relatively measuring angle sensors, an alignment of the internal steer angle with the measured steer angle is carried out, which measured steer angle is for example measured by an angle sensor installed in the steering column and is transmitted via CAN or Flexray. This is because the steer angle determined or calculated internally within the system cannot be unequivocally assigned a steering direction. Furthermore, the magnitude thereof may deviate significantly from the physical steer angle. Therefore, an alignment or a synchronization of the two steer angles has proven to be expedient. In the measured steer angles, however, there are often non-linear disturbances in the form of hystereses. Duringan alignment of the steer angles, therefore, the influence of hystereses should be compensated as fully as possible.
The present invention should permit compensation of angle errors, which arise on account of hysteresis, during the synchronization of a steering-system-internal steer angle with an external steer angle sensor.